Abstract
Optical Solar Reflectors (OSR) are fully light-reflective materials, which are used in satellite panels that bonded with metallic sheets with a layer of silicon type adhesive. During the bonding process, entrapping of air bubbles in the bondline is the main problem, and the detection of air bubbles is crucial for the thermal integrity of the panel. The inspectability investigation established in this work is a complete methodology that consists of the determination of the applicable NDT method, parameter optimization, reference specimen design, and most importantly, execution of the POD analysis for the detection reliability to implement the method into post-manufacturing NDI operations of OSR panels. A comprehensive comparison of conventional and advanced inspection methods were performed in this study, including sonic, ultrasonic, radiographic and thermographic techniques. After trials on generic scale panels, high sensitivity surfaces of OSR and large density differences of bonded elements lead to the selection of the lockin thermography technique. Next, an appropriate reference specimen was designed for the POD approach with thermally representative artificial defects. The results show that the lock-in thermography technique can detect air bubbles at the adhesive layer for sizes larger than 20 mm2 with a probability of detection of 90% at a confidence level of 95%.
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